1. Field of the Invention
The present invention relates to a battery module and a method of making the same. More particularly, the present invention relates to a battery module including a plurality of unit batteries and at least one end plate, wherein the battery module is configured to provide reduced weight and/or reduced likelihood of deformation of the end plate, and a method of making the same.
2. Description of the Related Art
Batteries may be manufactured in a wide variety of forms and may employ any of a number of technologies. Generally, batteries may be classified as single-use, i.e., primary, or rechargeable, i.e., secondary, batteries. Generally, secondary batteries may be charged and discharged, unlike primary batteries. Low capacity batteries having a single cell may be used for small electronic devices such as mobile phones, notebook computers, camcorders, etc. High capacity secondary batteries, which may be constructed by connecting a plurality of cells into a package form, may be used to high power equipment such as motors, etc., e.g., drive motors of hybrid electric vehicles (HEVs).
Secondary batteries may be manufactured in various shapes, e.g., cylindrical and rectangular shapes. The secondary batteries (hereinafter referred to as unit batteries) may be serially connected to create a battery module. The unit battery may include an electrode group having positive and negative electrodes that are disposed adjacent to each other with a separator interposed therebetween. A case may be provided, the case including space for enclosing the electrode group, which may be combined with a cap assembly to close the case. Positive and negative terminals, which may be electrically connected to positive or negative collectors, respectively, in the electrode assembly, may project through the cap assembly in order to allow for external electrical connections.
The unit batteries may be arranged so that neighboring positive and negative terminals alternate, in order to simplify electrical connections. A conductor may be connected to neighboring positive and negative terminals, e.g., using nuts affixed to threaded terminals, to electrically connect the unit batteries with one another.
A battery module may include from a few to tens of unit batteries. A plurality of unit batteries may be assembled in a stack and may be clamped by one or more end plates, i.e., such that an end plate is disposed against an outer side of the first and/or last unit battery in the stack. Two end plates may be located at the outermost sides of the unit batteries and the end plates may be fixed together to clamp the stack by using connecting rods attached to the end plates.
During operation of the battery module, insides of the unit batteries may swell due to overcharge or overdischarge. Swelling loads may accumulate in the stacked unit batteries and may be applied to the end plates, thereby causing bending deformation of the end plates. The bending deformation of the end plates may be caused by, e.g., stress concentration due to inhomogeneous contact between the connecting rods and the end plates.
It will be appreciated that bending deformation of an end plate may be reduced by increasing the strength of the end plate. However, such an increase in strength is generally achieved by using a thicker end plate, which may result in increased weight and cost of the battery module. Accordingly, there is a need for a battery module configured to reduce or eliminate bending deformation of the end plate without undue increases in weight.